I am using OpenCV 2.4.8 and Visual Studio 2013 to run the following simple VideoCapture program. The program is intended to capture the video from the webcam and display it.
However, the program works fine only for the FIRST TIME (after signing in windows), and doesn't work second time.
The problem I get on debugging is :
After executing this line - "bool bSuccess = cap.read(frame);" frame variable is still NULL.
#include "stdafx.h"
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
char key;
int main(int argc, char* argv[])
{
VideoCapture cap(0); // open the video camera no. 0
if(!cap.isOpened()) // if not success, exit program
{
cout << "Cannot open the video file" << endl;
return -1;
}
double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the video
cout << "Frame size : " << dWidth << " x " << dHeight << endl;
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
Mat frame;
while(1)
{
bool bSuccess = cap.read(frame); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
cout << "Cannot read a frame from video file" << endl;
break;
}
imshow("MyVideo", frame); //show the frame in "MyVideo" window
if(waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
{
cout << "esc key is pressed by user" << endl;
break;
}
}
return 0;
}
This happen because the camera is not correctly closed after first instance of program. You should try to close the console by esc button and not by clicking X.
Could you try and read more than a single frame before breaking the loop? This may be similar to this problem, where a corrupted first frame / slow camera set up was the only problem.
Unable to read frames from VideoCapture from secondary webcam with OpenCV
Related
I'm currently getting the webcam feed of my laptop using VideoCapture cap(0) function and then display it in a Mat frame. What I want to do next is whenever I press a key 'c' for example, it takes the screenshot of the frame and save it into a folder as a JPEG image. However I have no idea on how to do so. Help is much needed, thank you.
I have spent several days searching the internet for the right solution with simple keyboard input. Ther was allways some leg / delay while using cv::waitKey.
The solution i have found is with adding Sleep(5) just after the capturing the frame from webcam.
The below example is a combination of different forum threads.
It works without any leg / delay. Windows OS.
Press "q" to capture and save the frame.
There is a webcam feed always present. You can change the sequence to show the captured frame / image.
PS "tipka" - means "key" on the keyboard.
Regards, Andrej
#include <opencv2/opencv.hpp>
#include <iostream>
#include <stdio.h>
#include <windows.h> // For Sleep
using namespace cv;
using namespace std;
int ct = 0;
char tipka;
char filename[100]; // For filename
int c = 1; // For filename
int main(int, char**)
{
Mat frame;
//--- INITIALIZE VIDEOCAPTURE
VideoCapture cap;
// open the default camera using default API
cap.open(0);
// OR advance usage: select any API backend
int deviceID = 0; // 0 = open default camera
int apiID = cv::CAP_ANY; // 0 = autodetect default API
// open selected camera using selected API
cap.open(deviceID + apiID);
// check if we succeeded
if (!cap.isOpened()) {
cerr << "ERROR! Unable to open camera\n";
return -1;
}
//--- GRAB AND WRITE LOOP
cout << "Start grabbing" << endl
<< "Press a to terminate" << endl;
for (;;)
{
// wait for a new frame from camera and store it into 'frame'
cap.read(frame);
if (frame.empty()) {
cerr << "ERROR! blank frame grabbed\n";
break;
}
Sleep(5); // Sleep is mandatory - for no leg!
// show live and wait for a key with timeout long enough to show images
imshow("CAMERA 1", frame); // Window name
tipka = cv::waitKey(30);
if (tipka == 'q') {
sprintf_s(filename, "C:/Images/Frame_%d.jpg", c); // select your folder - filename is "Frame_n"
cv::waitKey(10);
imshow("CAMERA 1", frame);
imwrite(filename, frame);
cout << "Frame_" << c << endl;
c++;
}
if (tipka == 'a') {
cout << "Terminating..." << endl;
Sleep(2000);
break;
}
}
// the camera will be deinitialized automatically in VideoCapture destructor
return 0;
}
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
int main(int argc, char* argv[])
{
VideoCapture cap(0); // open the video camera no. 0
if (!cap.isOpened()) // if not success, exit program
{
cout << "ERROR: Cannot open the video file" << endl;
return -1;
}
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the video
cout << "Frame Size = " << dWidth << "x" << dHeight << endl;
Size frameSize(static_cast<int>(dWidth), static_cast<int>(dHeight));
VideoWriter oVideoWriter ("D:/MyVideo.avi", CV_FOURCC('P','I','M','1'), 20, frameSize, true); //initialize the VideoWriter object
if ( !oVideoWriter.isOpened() ) //if not initialize the VideoWriter successfully, exit the program
{
cout << "ERROR: Failed to write the video" << endl;
return -1;
}
while (1)
{
Mat frame;
bool bSuccess = cap.read(frame); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
cout << "ERROR: Cannot read a frame from video file" << endl;
break;
}
oVideoWriter.write(frame); //writer the frame into the file
imshow("MyVideo", frame); //show the frame in "MyVideo" window
if (waitKey(10) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
{
cout << "esc key is pressed by user" << endl;
break;
}
}
return 0;
}
I am developing this project using Visual Studio 2012 express and opencv_2.4.9 and windows 7 x64.
But, this code is not working.
Just write out this message "ERROR: Failed to write the video".
Use try, catch to see if you can get a more detailed error message.
One thing I remember when writing videos is that you need to verify you have the codecs installed and in the correct directory or added as a PATH environment variable.
opencv_ffmpeg.dll was the issue for me, and making sure it was in the correct directory and being renamed to opencv_ffmpeg249.dll
Using the code below, I am trying to create an app in C++ with OpenCV + Raspicam. This app should stream video in real time from the RasPi camera model connected to my Pi to an Xwindow.
I get the following error on compile:
videofeed.cpp: In function ‘int main(int, char**)’:
videofeed.cpp:36:37: error: ‘cv::imread’ is not a member of ‘raspicam::RaspiCam_Cv’
How do I remedy this?
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/videoio.hpp"
#include <iostream>
#include </home/pi/raspicam-0.1.3/src/raspicam_cv.h>
using namespace std;
int main ( int argc,char **argv ) {
raspicam::RaspiCam_Cv Camera;
cv::Mat image;
int nCount=100;
//set camera params
Camera.set( CV_CAP_PROP_FORMAT, CV_8UC1 );
//Open camera
cout<<"Opening Camera..."<<endl;
if (!Camera.open())// if not success, exit program
{
cout << "Cannot open the video cam" << endl;
return -1;
}
double dWidth = Camera.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames o$
double dHeight = Camera.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frame$
cout << "Frame size : " << dWidth << " x " << dHeight << endl;
cv::namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
while (1)
{
cv::Mat frame;
bool bSuccess = Camera.cv::imread(frame); // get a new frame from camera
if (!bSuccess) //if not success, break loop
{
cout << "Cannot read a frame from video stream" << endl;
break;
}
cv::imshow("MyVideo", frame); //show the frame in "MyVideo" window
if (cv::waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' ke$
{
cout << "esc key is pressed by user" << endl;
break;
}
}
return 0;
}
///////////////////////////////////////////////////////////////////////////////////
bool bSuccess = Camera.cv::imread(frame); is an error,there is no imreadfunciton in raspicam::RaspiCam_Cv.If you want grub a frame,you can use function grub and than retrieve .
For example:
Mat img;
camera.grab();
camera.retrieve(img);
You can see the declaration:
/**
* Grabs the next frame from video file or capturing device.
*/
bool grab();
/**
*Decodes and returns the grabbed video frame.
*/
void retrieve ( cv::Mat& image );
Also ,you can get example in:https://github.com/cedricve/raspicam
I tried the following code for capturing a video from my webcam:
#include "opencv2/highgui/highgui.hpp"
#include "opencv2/imgproc/imgproc.hpp"
#include <iostream>
#include <stdio.h>
#include <stdlib.h>
using namespace cv;
using namespace std;
int main()
{
VideoCapture cap(0); // open the video camera no. 0
if (!cap.isOpened()) // if not success, exit program
{
cout << "Cannot open the video cam" << endl;
return -1;
}
double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH); //get the width of frames of the video
double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT); //get the height of frames of the video
cout << "Frame size : " << dWidth << " x " << dHeight << endl;
namedWindow("MyVideo", CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
namedWindow("Changed", CV_WINDOW_AUTOSIZE);
while (1)
{
Mat frame;
bool bSuccess = cap.read(frame); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
cout << "Cannot read a frame from video stream" << endl;
break;
}
Mat imgH = frame + Scalar(75, 75, 75);
imshow("MyVideo", frame); //show the frame in "MyVideo" window
imshow("Changed", imgH);
if (waitKey(30) == 27) //wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
{
cout << "esc key is pressed by user" << endl;
break;
}
}
return 0;
}
Now here's my problem:
After debugging that program for the first time everything works as expected. But when debugging for a second time (after changing some lines in the code) it cannot read from the camera.
Does anyone have a hint for me how to solve that problem?
Thanks!
The code you posted seems to be working absolutely fine in my case, and the output is as intended.
However please make sure that your webcam is switched on before you run the program, this is important.
Since i have a YouCam client in my computer for the webcam, therefore it shows that i need to start youcam.
Since i dont have enough reputation to post an image, so please see the following link in order to view the output i got when webcam not already switched on.
http://i.imgur.com/h4bTZ7z.png
Hope this helps!!
I am trying to run a opencv program. I have configured opencv accordingly but I am getting the Visual Studio 2012 error "The application was unable to start correctly (0xc0000007b)."
Following is the code I am trying to run.
#include "opencv2/highgui/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
int main(int argc, char* argv[])
{
VideoCapture cap(0); // open the video camera no. 0
if (!cap.isOpened()) // if not success, exit program
{
cout << "Cannot open the video file" << endl;
return -1;
}
//get the width of frames of the video
double dWidth = cap.get(CV_CAP_PROP_FRAME_WIDTH);
//get the height of frames of the video
double dHeight = cap.get(CV_CAP_PROP_FRAME_HEIGHT);
cout << "Frame size : " << dWidth << " x " << dHeight << endl;
namedWindow("MyVideo",CV_WINDOW_AUTOSIZE); //create a window called "MyVideo"
while (1)
{
Mat frame;
bool bSuccess = cap.read(frame); // read a new frame from video
if (!bSuccess) //if not success, break loop
{
cout << "Cannot read a frame from video file" << endl;
break;
}
imshow("MyVideo", frame); //show the frame in "MyVideo" window
//wait for 'esc' key press for 30ms. If 'esc' key is pressed, break loop
if (waitKey(30) == 27)
{
cout << "esc key is pressed by user" << endl;
break;
}
}
return 0;
}
You are probably not including all of your libraries properly. Use Dependency Walker to check whether you are missing anything.